Navigational aides, such as those devices used in automobiles to assist drivers in locating destinations, have become very popular in recent years. These navigational aides work by receiving satellite signals from systems such as the Global Positioning System (GPS). GPS consists of 24 satellites that orbit the earth and transmit signals to these navigational aides. A navigational aide processes these signals to determine, for example, the location of a driver and, based on the driver's location, the navigational aides may provide directions to the driver's destination. In addition to navigational devices, GPS provides means for automatic vehicle location systems, aircraft landing systems, and precision timing systems. These devices have both commercial and military applications.
However, the satellite signals on which these devices rely are transmitted at a very low power level and are therefore susceptible to unintentional and intentional interference. Sources of unintentional interference include cellular phones and television stations transmitting antennas. Intentional interference (jamming) is accomplished by intentionally producing signals to interfere with the satellite signals transmitted.
When interference occurs, the performance of devices that rely on the satellite signals degrades. To maintain or improve the performance of these devices in the presence of interference, GPS receivers must be designed to cancel or minimize the interference.
For a significant reduction of the effects of interference to a desired satellite signal, a hardware implementation of digital filters operating on analog-to-digital sampled data from the satellite receiver's intermediate frequency may be required. The digital filters require numerical coefficients that are derived from the incoming sampled data and are applied to the filters in real-time. However, in conventional systems the hardware needed to store the sampled data is very costly and computationally inefficient. Therefore, there is a need for a GPS receiver that may cancel or minimize interference in a cost effective and computationally simplified manner.